The present disclosure relates to horizontal directional drilling (“HDD”) and, more particularly, to an improved reamer device useful for expanding and conditioning a previously drilled pilot bore.
Horizontal directional drilling (“HDD”), also termed “slant drilling,” is the practice of drilling non-vertical bores. A common application for HDD is for the installation of utility products such as underground wiring, small bore piping, cable bundles, and the like. The HDD process typically begins with drilling a pilot bore along a desired underground path. Next, the pilot hole is enlarged to a desired diameter and its walls conditioned by passing a larger cutting tool, sometimes termed a “reamer” or “back reamer,” back through the pilot hole. Finally, the product is installed in the enlarged hole by way of being pulled behind the reamer as the drill string is retracted from the reamed bore.
As one of ordinary skill in the art would recognize, when drilling a pilot bore the drill string is pushing forward, thereby facilitating a percussion cycle with a hammer component and a slidably engaged drill bit on the leading end. The hammer in an HDD drill string of this sort is not able to “run on cushion,” meaning that the reciprocation of the hammer will cease upon retraction of the drill string due to a resulting “open blow” alignment of internal air passages. Moreover, when the drill string is retracted, the slidably engaged drill bit is dragged along behind in a fully extended position that is out of reach of the hammer (the fully extended position of the drill bit correlates with the “open blow” alignment of the internal air passages).
Because a reamer is being pulled back through a bore, as opposed to being pushed like a drill bit, the reamer cuts and expands the walls of the bore by rotating cutting wheels. Also, the reamer may pull product via a product pulling feature. As the drill string is retracted, pressurized fluid is supplied from the drill string to the shaft of the reamer and up to the cutting wheels. The pressurized fluid provides a motive force for causing the cutting wheels to turn as the reamer is retracted.
The work of reaming a pilot bore is accomplished in the prior art via both pulling a relatively large reamer back through a relatively small pilot bore coupled with the cutting action of the cutting wheels. Notably, because the addition of a percussion force may improve the efficiency of a back reaming process, there is a need in the art for a reamer that is configured to work with a hammer component. More specifically, there is a need in the art for a reamer configured to promote the percussive cycle of a hammer component when the drill string is being retracted.